Radio pulse-echo system



2 Sheets-Shee't 1 Dec. 9, 1947.

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Patented Dec. 9, 1947 RADIO PULSE-ECHO SYSTEM Simeon I. Tourshou,

Philadelphia,

Pa., and

Robert Trachtenberg, Camden, N. J., assignors to Radio Corporation ofAmerica, a corporation of Delaware Application December 24, 1943, SerialNo. 515,496

6 Claims. (Cl. 250-27) Our invention relates to pulse-echo radio systemsand particularly to the production of electrical pulses.

One object of the invention is to provide an improved and simplifiedcircuit for producing two groups of periodically recurring pulses.

Another object of the invention is to provide an improved method of andmeans for producing a delayed electrical pulse.

A further object of the invention is to provide an improved method ofand means for producing two groups of periodically recurring pulseswhich have a fixed time relation to each other.

A further object of the invention is to provide a receiver that willdraw a comparatively small amount of +3 or high voltage direct current.

In one embodiment of the invention a circuit is provided for producingperiodically recurring narrow pulses for pulse modulating a radiotransmitter and for producing periodically recurring pulses of greaterwidth to function as gate pulses for the pulse receiver. These twogroups of pulses are produced by means of a blocking oscillator or thelike which applies very wide pulses to a pulse forming delay line ornetwork to charge the capacitors of the line during each wide pulse andwhich also applies the very wide pulses to a separate capacitor tocharge it also during each blocking oscillator pulse. At about the peakof each blocking oscillator pulse a gas or vapor tube, which isconnected for discharging said line and said capacitor, is ignited by adelayed blocking oscillator pulse so that the pulse forming line and theseparate condenser discharge therethrough. This produces a "gate pulsewhich appears at the end of the pulse forming line. It also produces anarrow transmitter modulating pulse which appears across the secondaryof a transformer that is connected in series with said separatecapacitor and said vapor tube.

Also, according to one feature of the invention, the pulse forming lineis so connected to a delay network that the gate pulse is retarded thedesired amount without affecting the operation of the pulse formingline.

Other objects, features and advantages of .the invention will appearfrom the following description taken in connection with the accompanyingdrawing in which Figure 1 is a circuit and block diagram of a pulse-echosystem embodying the invention,

Figure 1a is a group of graphs illustrating the operation of the systemof Fig. 1, and

Figures 2 to 6 are graphs illustrating the op- 2 eration of the pulseforming circuits shown in Fig. 1.

In the several figures, similar graphs are indicated by similarreference characters.

Fig. 1 shows the invention applied to a pulseecho system comprising aradio pulse transmitter oscillator ID, a radio pulse receiver ll, anintermediate-frequency amplifier l2, a second detector and videoamplifier unit l3, and a suitable indicator l5 for indicating thereception of reflected pulses. The amplifier I2 is adjusted so that itwill pass received signals only during the occurrence of a gate pulse il which, in the example illustrated in the drawing, is applied withpositive polarity to the screen grid of an intermediate-frequencyamplifier tube l2a.

In a preferred receiver the I.-F. amplifier comprises a plurality ofL-F. amplifier tubes in cascade and the gate pulse I4 is applied to thescreen grids of all these tubes except one or more which may be the lastL-F. tube which has a manual gain control voltage applied to its screengrid. It will be noted that there is no D.-C. voltage applied to thescreen grids of the I.-F. tubes (with the exception of the last I.-F.tube) with the result that there is a substantial saving in the +3 powersupply since it does not have to supply screen grid and anode currentscontinuously.

The oscillator H3 is modulated by a voltage pulse l 6 which appearsacross the secondary of a transformer H. The apparatus for producing thegate pulse [4 and the modulating pulse It comprises a suitable pulseproducing oscillator such as a freerunning or self-oscillatory blockingoscillator l8 which applies wide positive voltage pulses I9 (Fig. 2) tothe anode 2i of a gas or vapor tube 22 such as a Thyratron.

The blocking oscillator i8 is of conventional design and comprises avacuum tube 23, a feedback transformer 24, grid leak resistors 26 and 21and a grid capacitor 28 connected between the junction point ofresistors 26 and 21 and a point on the secondary of the transformer 24.A source of sine wave voltage may be substituted for the blockingoscillator 18 if desired.

The high potential end of the secondary of transformer 24 is connectedthrough resistors 3| and 32 to the anode 2| of the vapor tube 22 forapplying to the anode 2| a positive pulse 19 (Fig. 2). The same positivepulse 19 is applied across a resistor 33 and a capacitor 31 whereby adelayed pulse 20 (Fig. 3) appears across capacitor 31.

The delayed pulse 20 is applied to the grid 33 of the tube 22 through aresistor 34. The capacitor 31 and the resistor 36 are given such valuesas to introduce a suitable phase shift in the voltage pulse 20 to ignitethe tube 22 preferably a short time after the pulse l9 has reached itsmaximum positive value .as will be apparent from a comparison of Figs. 2and 3.

The gatepulse isproduced by" a. pulse forming'.

line 38 in the form of a network having series inductors and shuntcapacitors which has its inductor side connected to the anode 2| of thevaportube 22 so that it is charged by the. first portion of the blockingoscillator pulse l9. At the same time that the line 38 is being charged,acapacitor 39, which is connected between: the anodeZl of tube 22 andthe primary I'l'a of transformer I1; is also charged. An inductor H isalso included in series with the capacitor 39 and the. trans formerprimary Ila unless the leakage inductance of transformer l! is itselflarge enough-for-prmducing a pulse I6 of the desired width when thecapacitor 39 is discharged. Changing the amount of inductance in thecircuit in series with capacitor 39 changes the width of the pulseslfisince this pulse actually is 'one half-cycle of a damped sine wave in a.series resonant circuit as indicated by the'dotted' lines in Fig. 6.However, thisv damped. Wave is-substantially of the form shown. by thesolid linesince the tubes 40 and. 85 put' a low impedance load acrossthe secondary of. trans-- former H.

The delayed pulse 20- on the grid 33. of. the. vapor:tube'22.- causesthe tube 22 to ignite or: break down at about the time the blocking.oscillator: pulse l9. has applied a. maximum charge to. the;pulse-forming line 38' and to thecapacitor. 3.9;: When the tube 22'breaks down, it discharges. the. line 38 to forms. pulse Eta of awidth-or duration that is equal to the time required for: a wave. to.travel from one end of the line 3 8-:to the other end ofthe lineandback. In.the.example given. this pulse width is 3 ,4 microseconds.

The breakdown of vapor tube. 22 also. dis-- charges the capacitor- 39.through the inductor. M and the primary 'la.of transformerlkwhereby-thenarrow pulselfi is produced. In the-pres.- en't -example' the widthofpulselfi is. micro second. By making transformer IT a. voltage step uptransformer, the pulse l6. mayibeimade of high enough amplitude so thatwhen. applied to the-anodes of the tubes 49 and455of5th'eradi'ofrequency oscillator H]. the oscillator" oscillatesduring. the application of the pulse. In.the.ex ample illustrated,there. is no D. 0.. voltage on the oscillator anodes. The oscillator- Iis: conventional in= design having a tuned. line:.50, .inxtheplate-circuit and: having the cathodesof tubes 46 and 35 operated aboveground; potentialat the radio frequency.

The modulating pulse ifi'preferablyt'is'z applied to" the oscillator l0.through resistor-capacitor biasing elements 43- and Ml, respectively;and: through a radio-frequency choke coil 46'; Dure ing the pulse it:the. D. C. anodecurrent of the. oscillator tubes. 40 and 45': flows.throughatheebias ing elements 43. and M" to charge the: capacitor itwhereby the anodes of tubes iiiand iiiib'ecome negativesomewhat beforethe endof the modulation' pulse 15 resulting in a sharper cut-=01? oftheoscillations; also, they are held negative-long enough topreventanyp'ositive components that might follow the pulse l from"energizing the oscillator lfl.

Referring again to the production of the gate pulse I 411-, the pulse il from the pulse-forming line38 is delayed the desiredamount by'a delay"network 41 which comprises series inductors and shunt capacitors, theamount of delay being about one and one-half microsecond, for example,as indicated in Fig. 5.

The output end of the delay line 41 is connected to a transformer 48shunted by a resistor 49 towprovide a non-reflecting termination. Also,

means preferablyare provided for sloping the front edge of the gatepulse 14 whereby the sensitivity or gain of the intermediate frequencyamplifier. 12 is the greatest when reflected pulses l'iia (Fig. 1a) arereceived from the more distant part: of the. pulse reception region.This also results inan improved signal-to-noise ratio. The pulse slopingmeans may comprise a, resistor 5| and a capacitor 52- connected inseries with each otherand-inshunt to..the transformer 48. It may benoted that the gain of the receiver as plotted againsttime has a greaterslope than that of the gate pulse [4 since this pulse is applied to apluralityr of I; F. amplifier: tubes-in-cascada- In order" that the twolinesor networks 38:.and. t! shall perform their pulse forming andpulse. delaying. functions independentlyv ofeach other, the seriesinductor sideof network l'lisconnectedi to that side. of. networkrSBwhich-isopposite-its. series inductor side. The end of. thenetwork fltremote from the charging endisopen-circuited: and, therefore,reflecting. Theimpedance 'loob' ing'into the input endv ofthe:networlcl'l 'issubstantially equal to; the surge. impedance of; the; network 38.

We claim as our: invention:

1. In a pulse-echo system; meansvforproducing-periodically recurringelectrical voltage-waves; each. of, positive polarity and; otcomparatively longduration, a. pulse-forming.-v delay: line and: a gasor vapor. tube-connectedto. discharge-said line for: forming; a; pulse.when said. tube is: ignited; a. capacitor and apulse-formingcircuitconn'ected; in: series: with: the cathode-anode impedance oi:said-tube, means .for applying said voltage simultaneously tosaidlinapto the anode-of. said tube andito said capacitor, and:means'foridise' charging; said line and said. capacitor. through said.tube: after each has. been charged; Icy-one of .said voltage waves.

2; In a pulse-echo systemnmeans, for producing: periodically recurring,electrical. voltage waves eachwof positivepolarity and-ofi comparestively; long. duration, a pulse-forming; delay. line anda gas or vaportube connected tor discharge said linewhensaid tube; is ignited;,.capacitor anda pulse-forming circuit; connected miseries. with: thecathode-anodeimpedance. of said tube; means forapplying. said. voltagewaves-simultaneously to said. line, to .the anode of said: tube and.tesaid capacitor, and means'for.also..appiye ing said. voltage wavesto. the control electrode of said tube. slightlydelayedwith.respectitoithe voltage .waves. appliedjto said anodawhereby,said line. and. said' capacitor. are both discharged through said tubeafter being chargedlby-on'epf said voltage waves;

3; Irrapulse-echo system; meansfor'produm ing periodically recurringelectrical voltagewaves each" of positivepolarity and of comparativelylong duration, pulse-forming delay 'lineand a gas 1 or vapor" tubeconnected to" discharge said line to form a pulse when said tube isignited;- a' capacitor-"and an inductor connected in series withthe--ca-thode-anode impedance of sa-idtube to" form a pulse when saidcapacitor is diseliarged, means for applying said" voltage wavesSim-uhtaneously-to-saidline; to theanodeof said tube and to saidcapacitor, and means for also applying said voltage waves to the controlelectrode of said tube slightly delayed with respect to the voltagewaves applied to said anode whereby said line and said capacitor areboth discharged through said tube after being charged by one of saidvoltage waves,

4. In combination, a pulse-forming delay network comprising seriesinductors and shunt capacitors and having input terminals, at one end ofthe network and a reflecting termination at the other end of thenetwork, one of said terminals being common to both ends of the network, a second delay network comprising series inductors and shuntcapacitors and having input terminals and output terminals and having asubstantially non-reflecting termination at its output end, saidterminals of the second network including a terminal that is common toboth ends of the network, the common terminal of one of said networksbeing connected to the input terminal of the other network which is notcommon to both ends of the network, and means connected to the tworemaining input terminals of the two networks for periodically chargingand discharging said first network whereby periodically recurringdelayed pulses are produced.

5. In combination, a pulse-forming delay network comprising seriesinductors and shunt capacitors and having input terminals at one end ofthe network and a reflecting termination at the other end of thenetwork, one of said terminals being common to both ends of the network,a second delay network comprising series inductors and shunt capacitorsand having input terminals and output terminals and having asubstantially non-reflecting termination at its output end, saidterminals of the second network including a terminal that is common toboth ends of the network, the common terminal of said first networkbeing connected to the input terminal of the other network which is notcommon to both ends of the network, and means connected to the tworemaining input terminals of the two networks for periodically chargingand discharging said first network whereby periodically recurringdelayed pulses are produced at the output terminals of said secondnetwork.

6. In combination, a pulse-forming delay network comprising seriesinductors and shunt capacitors and having input terminals at one end ofthe network and a reflecting termination at the other, end of thenetwork, one of said terminals being common to both ends of the network,a second delay network comprising series inductors and shunt capacitorsand having input terminals and output terminals and have a substantiallynon-reflecting termination at its output end, the input impedance of thesecond network being substantially equal to the surge impedance of thefirst network, said terminals of the second network including a terminalthat is common to both ends of the network, the common terminal of saidfirst network being connected to the input terminal of the other networkwhich is not common to both ends of the network, means connected to thetwo remaining input terminals of the two networks for'charging saidfirst network, and means for periodically discharging said first networkwhereby periodically recurring delayed pulses are produced at the outputterminals of the second network.

SIMEON I. TOURSHOU. ROBERT TRACHTENBERG.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,189,549 Hershberger Feb. 6,1940 1,924,174 Wolf Aug. 29, 1933 2,223,995 Kotowski et al Dec. 3, 19402,281,441 Horton et a1. Apr. 28, 1942 2,309,525 Mohr Jan. 26, 1943

